U.S. patent application number 13/515883 was filed with the patent office on 2012-10-04 for method for purifying compounds containing amino groups.
This patent application is currently assigned to BASF SE. Invention is credited to Burkhard Ernst, Wolfgang Siegel, Martin Volkert.
Application Number | 20120253076 13/515883 |
Document ID | / |
Family ID | 43901204 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120253076 |
Kind Code |
A1 |
Volkert; Martin ; et
al. |
October 4, 2012 |
METHOD FOR PURIFYING COMPOUNDS CONTAINING AMINO GROUPS
Abstract
Method for purifying compounds (I) containing amino groups from
a polar phase A, where (I) is converted by reaction with an
aldehyde or ketone (II) into the corresponding imine (III) which is
insoluble or sparingly soluble in the polar phase A, and then the
imine (III) is converted to a nonpolar phase B and separated off
from phase A, and then the compound containing amino groups is
recovered from the imine (III).
Inventors: |
Volkert; Martin;
(Ludwigshafen, DE) ; Ernst; Burkhard; (Speyer,
DE) ; Siegel; Wolfgang; (Limburgerhof, DE) |
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
43901204 |
Appl. No.: |
13/515883 |
Filed: |
December 13, 2010 |
PCT Filed: |
December 13, 2010 |
PCT NO: |
PCT/EP2010/069523 |
371 Date: |
June 14, 2012 |
Current U.S.
Class: |
564/497 |
Current CPC
Class: |
C07C 209/84 20130101;
C07C 45/516 20130101; C07C 209/84 20130101; C07C 249/02 20130101;
C07C 249/02 20130101; C07C 211/09 20130101; C07C 251/24
20130101 |
Class at
Publication: |
564/497 |
International
Class: |
C07C 209/84 20060101
C07C209/84; C07C 211/09 20060101 C07C211/09 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2009 |
EP |
09179624.3 |
Claims
1-7. (canceled)
8. A method for purifying a compound (I) containing amino groups
from a polar phase A, where i) converting compound (I) through
reaction with an aldehyde or ketone (II) into the corresponding
imine (III) which is insoluble or sparingly soluble in the polar
phase A and ii) then converting the imine (III) to a nonpolar phase
B and iii) separating off from phase A, and iv) then the compound
containing amino groups is recovered from the imine (III).
9. The method according to claim 8, wherein the compound (I)
containing amino groups is a dialkylamine.
10. The method according to claim 9, wherein the dialkylamine is
1,5-diaminopentane.
11. The method according to claim 8, wherein the separation in iii)
takes place by an extraction process.
12. The method according to claim 10, wherein the separation in
iii) takes place by an extraction process.
13. The method according to claim 8, where, in i), benzaldehyde is
used as (II).
14. The method according to claim 12, where, in i), benzaldehyde is
used as (II).
15. The method according to claim 8, where, in iv), the isolation
of (I) from (III) is effected by adding an acid.
16. The method according to claim 14, where, in iv), the isolation
of (I) from (III) is effected by adding an acid.
17. The method according to claim 15, where the acid is added in
equimolar amounts based on (I).
18. The method according to claim 16, where the acid is added in
equimolar amounts based on (I).
Description
[0001] The present invention relates to a method for purifying
compounds containing amino groups, in particular alkylamines or
alkyldiamines, which are present together with impurities and
by-products in a polar phase. Of particular suitability is the
method for purifying compounds containing amino groups which have
been prepared by fermentation and which, at the end of the
preparation process, are present in an aqueous phase together with
constituents of the fermentation medium.
BACKGROUND OF THE INVENTION
[0002] Compounds containing amino groups are important basic
substances in the chemical industry. For example, alkylamines and
alkyldiamines are used in the production of polyamides, polyureas
or polyurethanes and also copolymers thereof.
[0003] The fermentative or enzymatic production of alkyldiamines,
for example of diaminopentane (DAP) by decarboxylation of lysine
has been known for a relatively long time. In this connection,
various methods for isolating the product of value from the
fermentation broth are described.
[0004] Thus, for example, EP-A-1 482 055 describes the enzymatic
decarboxylation of lysine in the presence of a dicarboxylic acid
for establishing the pH during the reaction. The DAP dicarboxylate
produced during the preparation is isolated by firstly decoloring
the solution containing substance of value with activated carbon,
concentrating it and crystallizing out DAP dicarboxylate by means
of a cooling crystallization.
[0005] JP 2004-222 569 describes the preparation of DAP using an
L-lysine decarboxylase-expressing coryneform bacterium, adjustment
of the culture supernatant to pH 12 and extraction of DAP with a
polar organic solvent.
[0006] JP 2004-000 114 describes the preparation of DAP by reacting
highly concentrated L-lysine monohydrochloride with L-lysine
decarboxylase-expressing E. coli cells, adjusting the reaction
solution to pH 3 and extraction of the reaction product with a
polar organic solvent and subsequent distillation.
[0007] WO 2009/92793 describes a method for isolating
1,5-diaminopentane (DAP) from a DAP-containing fermentation broth,
where the fermentation broth is a) alkalized, b) thermally treated,
c) DAP is extracted with an organic extractant, and d) DAP is
isolated from the separated-off organic phase.
[0008] However, particularly the methods known from the prior art
and based on an extraction of DAP with the help of an organic
solvent are burdened with the disadvantage that the yield of
substance of value is not optimal and especially the extraction
step proceeds too slowly and the overall method is therefore too
time-consuming, which is a major disadvantage for application of
the preparation on an industrial scale.
SUMMARY OF THE INVENTION
[0009] The object of the present invention is therefore to further
improve the isolation of compounds containing amino groups from
fermentation broths. In particular, the yield of substance of value
should be further increased and the required time expenditure for
the isolation, in particular the solvent-based extraction, should
be improved.
[0010] Surprisingly, this object has been achieved through
provision of a method for purifying compounds (I) containing amino
groups from a polar phase A, where [0011] i) (I) is converted
through reaction with an aldehyde or ketone (II) into the
corresponding imine (III) which is insoluble or sparingly soluble
in the polar phase A and [0012] ii) then the imine (III) is
converted to a nonpolar phase B and [0013] iii) is separated off
from phase A, and [0014] iv) then the compound containing amino
groups is recovered from the imine (III).
DETAILED DESCRIPTION OF THE INVENTION
Preferred Embodiments
[0015] The invention provides a method for purifying compounds (I)
containing amino groups from a polar phase A, where [0016] i) (I)
is converted through reaction with an aldehyde or ketone (II) into
the corresponding imine (III) which is insoluble or sparingly
soluble in the polar phase A and [0017] ii) then the imine (III) is
converted to a nonpolar phase B and [0018] iii) is separated off
from phase A, and [0019] iv) then the compound containing amino
groups is recovered from the imine (III).
[0020] In a first specific embodiment of the method for purifying
compounds (I) containing amino groups, alkyl derivatives which
carry one or more, preferably two or three, amino functions are
used as (I). In particular, mention may be made here of alkyl
derivatives having 1 to 10 carbon atoms, which may be present in
linear, branched or cyclic form. The method is particularly
advantageously used for diaminoalkyls, such as diaminopropane,
diaminobutane, diaminopentane, diaminohexane, diaminoheptane and
diaminooctane. In these specified compounds, the two amino groups
may be in any arrangement relative to one another, but are
preferably in 1,n position for a diamino-n-alkyl, i.e.
1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane etc.
[0021] Such diaminoalkyls are prepared by methods known to the
person skilled in the art. A preparation process which is used
advantageously for diamines such as 1,5-diaminopentane is the
fermentative or enzymatic preparation.
[0022] Here, at the end of the preparation process, the compound
(I) containing amino groups is usually present in an aqueous
fermentation medium in which, besides compound containing amino
groups and, if appropriate, by-products and starting materials,
also constituents of the nutrient medium and also metabolic
products are present. Such an aqueous fermentation medium is
referred to for example as polar phase A. Other examples of polar
phases A are water or aqueous solutions or polar organic solvent
such as lower alkyl alcohols or lower carboxylic acids or mixtures
of these polar organic solvents with water.
[0023] The compounds containing amino groups are generally readily
soluble in aqueous phases, especially at a low pH as a consequence
of (partial) protonation.
[0024] The compounds (I) containing amino groups are converted
through reaction with an aldehyde or ketone (II) to the
corresponding imine (III). (II) is advantageously selected such
that the formed (III) is insoluble or only sparingly soluble in the
polar phase A in which (I) is located.
[0025] The reaction of (I) with (II) to give (III) can be carried
out in a wide temperature range, preference being given to
temperatures between 20 and 50.degree. C. The imine formation is
improved by adding a base since, as the result of this, the
position of the equilibrium is shifted to the (III) side.
[0026] As aldehyde or ketone (II), it is possible to use any
desired aliphatic or aromatic aldehydes and ketones which are
capable of diimine formation with compounds carrying amino groups.
Those compounds (II) which reduce the solubility of the imines
(III) to be formed in the polar phase A in which the compounds
containing amino groups are located are advantageous.
[0027] Preferred aldehydes or ketones (II) are benzaldehyde,
valeraldehyde, cyclohexanone, methyl ethyl ketone, diisobutyl
ketone, 2-octanone and acetone, where, for the imine formation from
1,5-diaminopentane, benzaldehyde is particularly preferred.
[0028] The aldehyde or ketone (II) is usually used in equimolar
amounts or a slight excess (1-1.5 preferably 1-1.1 equivalents)
based on the amino groups in the compounds (I) containing amino
groups, in order to achieve a quantitative imine formation
(III).
[0029] However, since the aldehydes or ketones (II) can also serve
as solvents for the imines (III), it is also possible to use (II)
in a large excess based on (I) and then to separate off the formed
imines (III) in (II) as solvent.
[0030] In a step iii) of the method according to the invention, the
formed imine (III) is converted to a nonpolar phase B. Nonpolar
phase B is understood as meaning a phase which is not to a
noteworthy extent miscible with the polar phase A, and preferably
forms a phase separation to phase A.
[0031] Besides the aforementioned compounds (II), nonpolar phase B
can also nonpolar organic solvents such as ethers, medium- and
relatively long-chain alcohols, hydrocarbons, ketones, aldehydes,
aromatics.
[0032] Nonpolar phase B can be added as early as at the start of
step ii); however, it is also possible to carry out step ii)
without further solvents and only to add a nonpolar phase B after
imine formation (III) has taken place.
[0033] In a further step iii), the nonpolar phase B, which
comprises the imine (III), is separated off from the polar phase A.
This step is preferably carried out as an extraction and can be
operated continuously or discontinuously. Preference is given to a
discontinuous extraction at elevated temperature, i.e. between
30.degree. and 70.degree. C.
[0034] In one preferred embodiment, the extraction and/or the
subsequent phase separation is carried out discontinuously at
elevated temperature, the temperature being limited by the boiling
points of water and of the extractant and/or azeotropes that are
possibly formed. Using n-butanol as extractant, extraction and
phase separation could be carried out e.g. at about 25-90.degree.
C. or preferably at 40-70.degree. C. For the extraction, the two
phases are stirred until the partition equilibrium has been
established, e.g. over a period from 10 seconds to 2 hours,
preferred 5 to 15 min. The phases are then left to stand until the
phases have completely separated; this takes place preferably over
a period of 10 seconds to 5 hours, such as e.g. 15 to 120 or 30 to
90 minutes, in particular also at a temperature in the range of
about 25-90.degree. C. or 40-70.degree. C. in the case of
n-butanol.
[0035] The design in terms of apparatus of the extraction columns
which can be used according to the invention can be established by
the person skilled in the art for the phases to be separated in
each case in the course of routine optimization work. Of
suitability in principle are extraction columns without power input
or extraction columns with power input, such as e.g. pulsed columns
or columns with rotating internals. The person skilled in the art
can also, in the course of routine work, select the type and
materials of internals, such as sieve trays, and column packings,
for optimizing the phase separation in a suitable manner. The
theoretical principles of liquid-liquid extraction of small
molecules are generally known (cf. e.g. H.-J. Rehm and G. Reed,
Eds., (1993), Biotechology, Volume 3 Bioprocessing, Chapter 21,
VCH, Weinheim). The configuration of industrially applicable
extraction columns is described for example in Lo et al., Eds.,
(1983) Handbook of Solvent Extraction, John Wiley& Sons, New
York. Reference is expressly made to the disclosure of the above
textbooks.
[0036] The phase separation required for a successful extraction
can be positively influenced by changing the pH in the polar phase
A. As a rule, pH values of >12 achieve optimal mass transfer
into the nonpolar phase B.
[0037] If desired; after separating off the imine (III) from the
polar phase A, it can be further purified or concentrated at the
imine stage, for example by distillation, chromatography or
crystallization.
[0038] In a last step iv), the compounds (I) containing amino
groups are recovered from the imines (III). This back-reaction of
the imine formation takes place advantageously with the addition of
acid, it being possible to use here mineral acids or organic acids.
The back-reaction of the imine formation takes place particularly
readily with an equimolar addition of acid. Step iv) can be carried
out by means of steam distillation.
[0039] A particular embodiment uses those acids which can form
polyamides in a subsequent process with the compounds (I)
containing amino groups. Here, as a result of the purification
according to the invention of the compound (I) containing amino
groups, the monomeric "preproduct" consisting of carboxylic acid
and compound (I) containing amino groups can be simultaneously
provided for the still to be prepared polyamides. This embodiment
is preferably in the case of diaminoalkylene as (I) which are to be
reacted with dicarboxylic acids to give polyamides. Nonlimiting
examples of suitable dicarboxylic acids are succinic acid, glutaric
acid, adipic acid, pimelic acid, suberic acid, azelaic acid,
sebacic acid.
[0040] In the case of the compound containing amino groups
1,5-diaminopentane, preferred acids for this embodiment are sebacic
acid and adipic acid.
[0041] General information relating to the fermentative preparation
of 1,5-diaminopentane (DAP)
[0042] As regards the fermentative preparation of
1,5-diaminopentane, reference is made to WO 2009/92793. The
experiments described below refer to the DAP obtained in this way
by fermentation.
[0043] The fermentation broths, particularly those containing
L-lysine or DAP, obtained in this way usually have a dry mass of
from 3 to 20% by weight.
[0044] The fermentation broth is then further processed. Depending
on requirements, the biomass can be completely or partly removed
from the fermentation broth by separation methods, such as e.g.
centrifugation, filtration, decantation, flocculation or a
combination of these methods, or be left entirely therein.
Preference is given to separating off the biomass.
[0045] The fermentation broth can then be thickened or concentrated
using known methods, such as e.g. with the help of a rotary
evaporator, thin-film evaporator, falling-film evaporator, by
reverse osmosis, or by nanofiltration. If required, any salts
precipitated out by the concentration can be separated off for
example by filtration or centrifugation. The concentrated
fermentation broth can then be worked-up in the manner according to
the invention in order to obtain DAP. For the work-up within the
context of the present invention, such a concentration is possible,
but not absolutely necessary.
Experimental Part
Formation of Imine for the Purification of DAP
[0046] The imine formation (FIG. 1 using benzaldehyde as the
example) proceeds with the elimination of water. As a consequence
of the pH regulation in the fermentation, DAP is present in the
broth as sulfate, which leads during the imine formation to the
reduction in the pH and shifts the reaction back to the starting
material side. This makes the addition of a base necessary in order
to bring the reaction to completion.
##STR00001##
FIG. 1 Imine Formation
[0047] With benzaldehyde, the spontaneous deposition of an organic
product phase was observed. In principle, the reaction was
successful with the stoichiometric amount of benzaldehyde and then
led to products of up to 98.5 area % GC purity.
[0048] During the extraction of an alkaline fermentation broth with
methyl ethyl ketone, a mixture of imine, diaminopentane and water
was deposited. Phase separation was extraordinarily good in this
experiment. From the mixture it was possible to back-cleave
diaminopentane through a steam distillation with removal of the
azeotrope (but without defined reflux); it was largely retained in
the bottom.
[0049] The following were used successfully: cyclohexanone, methyl
ethyl ketone (MEK), diisobutyl ketone, benzaldehyde, valeraldehyde,
2-octanone, methyl isoamyl ketone, methyl isobutyl ketone.
Imine Formation with Benzaldehyde
[0050] In an experiment to determine the required amount of base,
212 g of fermentation broth with a DAP content of 6% were admixed
with 2 eq. of benzaldehyde and the product distribution and the pH
were determined as a function of the added amount of NaOH (fig.).
For this, after adding the respective amount of NaOH, a sample was
taken, the phases were separated and the aqueous and organic phases
were analyzed by GC and quantitative HPLC.
[0051] It was found that after adding 20 g of NaOH, the conversion
was virtually complete (benzaldehyde virtually consumed, barely DAP
in the water phase, GC of the upper phase 92.5% diimine); here, a
pH of 9.4 had been established in the mixture. Based on the PMDA
present in the fermentation broth, this corresponds to a feed
number of ca. 0.8 kg NaOH/kg DAP 100% strength, and is thus
somewhat more favorable than in the case of the extractive work-up,
but is nevertheless in the same order of magnitude. An experiment
for the continuous extraction of the diimine from a fermentation
broth in the rotary perforator initially proceeded with difficulty
due to a very sluggish distillation on account of the high boiling
point of the benzaldehyde (180.degree. C.), although it was found
that at a pH of 5.85, which is rapidly established after adding the
benzaldehyde, virtually no diimine could be extracted.
[0052] In the 4 ml iniplant reactor, from 4 kg of fermentation
broth (pH 13.5, DAP content 6.78% by weight) with the addition of 2
eq. of benzaldehyde, the desired imine could be isolated
quantitatively in high purity (753 g, 98.4 area % GC). Phase
separation took place spontaneously, but was only complete after 48
h--barely half of the product settied out from the water phase even
during this time. [0053] Apparatus: 4 l miniplant reactor, with pH
probe and pH meter [0054] Mixture: 4053.0 g of DAP broth GC % by
wt. 6.78 corresponds to 274.8 g of DAP 2.7 mol [0055] 572.9 g of
benzaldehyde (5.4 mot, 2 eq) [0056] Reaction: The fermentation
broth was introduced as initial charge at RT (stirrer 400 rpm). The
benzaldehyde is then metered in over the course of one hour.
Stirred overnight. pH 13. Has not changed during the reaction.
[0057] Work-up: The phases were separated. Organic phase (753.4 g),
aqueous phase (3880 g). 330 g of this organic phase was separated
only after ca. 48 h. [0058] Analytics: GC: method GC9-06-K.M imine
98.4 area %
[0059] In general, during the imine formation, states emulsified
with benzaldehyde are passed through, and only after largely
complete reaction is the phase separation acceptable again.
[0060] In order to improve and increase the rate of phase
separation, a series of experiments were undertaken with solvents.
For this, alkaline fermentation broths were admixed at room
temperature with a mixture of benzaldehyde and the solvent in
question and the phases were separated at elevated temperature
(Table 1).
TABLE-US-00001 TABLE 1 Amount Ex. of No. Solvent solvent Temp.
Remarks 1 Cyclohexane 100% 50.degree. C. cloudy phases -
clarification only after 48 h 2 Benzaldehyde 100% 60.degree. C.
homogeneous, readily separable 3 Benzaldehyde 50% 60.degree. C.
homogeneous, readily separable 4 2-Octanol 100% 60.degree. C. very
good phase separation. Incomplete conversion 5 1-Hexanol 100%
60.degree. C. very good phase separation, complete conversion 6
Cyclohexanol 100% 60.degree. C. very good phase separation,
complete conversion 7 Without 60.degree. C. acceptable phase
separation, slight mulm
[0061] For cyclohexane and toluene, moreover, experiments were
carried out in which, at 50.degree. C., the phase separation time
was investigated as a function of the progress of the
reaction--controlled via the added amount of NaOH and the
benzaldehyde used. Following phase separation, the aqueous phase
was replenished in each case through the metered addition of NaOH
to pH 10, benzaldehyde and solvent were freshly added, the mixture
was stirred for 15 minutes and pH and phase separation times were
measured. With toluene, phase separation times between 27 and 54
seconds were observed, the aqueous phases being cloudy at the start
and virtually clear at the end. The first organic phases contained
a very stable foam, which did not disintegrate even upon combining
the organic phases.
[0062] With cyclohexane, the phase separation times were between 35
and 110 seconds. The aqueous phases were generally less cloudy than
with toluene, but also in these organic phases, the formation of
very stable foams resulted (34224/28).
[0063] In a further experiment with 4 eq. of benzaldehyde, the
phase separation was investigated depending on the added amount of
NaOH. Here, the phase separation remained slow until the pH of 9
was reached and all of the PMDA had reacted to give the imine. This
was the case for an amount of 65 g of NaOH (50% strength), based on
the PMDA used this corresponds to a feed number of 0.6 kg/kg
PMDA.
[0064] The organic phase remained foamy until the reaction was
complete whereas then phase separation was good.
Cleavage of Imines
[0065] The imine formation is an equilibrium reaction in the
presence of water, and therefore it was the original idea to manage
the back-reaction in such a way that the carbonyl component being
released could be removed from the equilibrium as steam-volatile
compound by steam distillation. At the same time, the position of
the equilibrium is dependent on the pH, which was indeed also
observed even during the imine formation.
Benzaldehyde Imines
[0066] As a result of a stoichiometric amount of sulfuric acid, the
cleavage of the imine takes place smoothly in an aqueous mixture.
The back-cleaved benzaldehyde is deposited as an independent
organic phase and can be separated off.
[0067] As small cleavage experiments, in each case 15-20 g of imine
were distilled with water without further additives and also in the
presence of in each case 0.5 g of sulfuric acid, Lewatit S 1468
(strongly acidic ion exchanger), Lewatit CNP80 (weakly acidic ion
exchanger) and p-toluenesulfonic acid. In this connection, in no
case was a cleavage of the imine observed which extended beyond the
extent to be expected due to the catalyst acid.
[0068] The imine itself could not be distilled at 4 mbar at an oil
bath temperature up to 240.degree. C.
[0069] Since in the first exploratory experiments, in each case
condensed water phases were present which could possibly influence
the establishment of an equilibrium, in further experiments at
140-160.degree. C., water was slowly added dropwise or steam was
introduced. Here, firstly 5 mol % of sulfuric acid were used as
catalyst, and also a comparative experiment without catalyst was
carried out. The experiment with the dropwise addition of water
foamed to such an extent that some of the distillation bottom was
entrained into the distillate initial charge. The experiments with
the introduction of steam, on the other hand, proceeded in an
uncomplicated manner.
[0070] In the presence of 5 mol % of sulfuric acid as catalyst, a
mass decrease of the bottom from 117 to 86 g was observed, by GC
the diimine to 98.2% by weight. The cloudy distillate (767 g) was
extracted with methylene chloride; 4.9% diaminopentane and 7.1%
diimine were found in the extract. Ca. 10% of the diimine were thus
cleaved and a further 10% were distilled over. It could not be
differentiated whether the diimine distills over undecomposed by
the steam despite the high boiling point, or whether the
diaminopentane distilling over with the benzaldehyde in the initial
charge leads to the new formation of the imine. A control
experiment for the steam distillation of DAP from aqueous solution
revealed that DAP should be retained virtually completely by the
attached Vigreux column.
[0071] Without added sulfuric acid, 96% of the diimine used (117 g)
were recovered, of which 17% were present in the distillate (900
g). In order to be useful in practice, by using a column with
higher separation efficiency, the water/benzaldehyde azeotrope must
be separated off from the DAP if the diimine is not anyway passed
over undecomposed by the steam. In the bottom, no enrichment of
free DAP was observed, although analysis is difficult because under
the conditions of the HPLC, the diimine is partly back-cleaved to
free DAP, but on the other hand the GC method is not able to
separate PMDA and benzaldehyde on account of their identical
boiling point.
[0072] In summary, the benzylidene compound is obviously stabilized
so much that the shift in the equilibrium to the starting material
side as a result of steam distillation does not take place even in
the presence of catalytic amounts of acid.
[0073] Since, on the other hand, the back-cleavage was successful
through quantitative amounts of acid, it seemed obvious to use, as
acid for the cleavage of the imine, the dicarboxylic acid with
which the subsequent polymerization is intended. Following the
addition of 1 eq. of sebacic acid and steam distillation of the
benzaldehyde being released, the sebacate was retained in the
bottom. This salt could be further purified by recrystallization
from ethanol or butanol. The preparation of the DAP adipate with
adipis acid also succeeded in exactly the same way.
[0074] In a demonstration experiment, 175 g of imine (prepared from
a fermentation broth) with 121 g of sebacic acid in 1200 g of water
were subjected to an azeotropic distillation. The remaining residue
was taken up in ethanol, adjusted by azeotropic distillation to a
water value of <0.3% and a content of ca. 30% strength and
crystallized with inoculation at 50.degree. C. and cooling to
40.degree. C. in 2 h, and also to 20.degree. C. in a further 2 h.
During the crystallization, the acetyldiaminopentane, which was
present in the imine with ca. 1.5%, was depleted by about 213. Ca.
89% of a weakly yellowish colored crystallizate were obtained.
Recrystallization from ethanol led to no further improvement in the
color. A difficulty observed was that excess sebacic acid
precipitates out at too low a temperature. Precise determination of
the imine content and accurate adjustment of the stoichiometry are
advantageous for achieving a high purity.
##STR00002##
* * * * *